It is sometimes necessary or desirable to detect the occurrence and magnitude of a time-variant signal, as for example signals representing electrochemical activity, or signals derived from pressure pulses in hydraulic systems, or signals developed in response to variations in temperature (thermistor), or signals related to seismic activity, etc.
Traditionally the time-variant signal is passed through a diode to a capacitor for storage as a peak. However the common diode-capacitor system is not completely satisfactory. For example, the forward voltage drop across the diode is variable and indeterminate; also, the capacitor charge rate is affected by the output impedance of the driving circuit; also the capacitor discharge rate is affected by the input impedance of the following dircuitry; also, the time of occurrence of the peak is usually not ascertainable; also, the stored signal is not in readily usable digital form; additionally the stored signal "droops" in a time-dependent fashion.
At least one commercially available detector, the Burr-Brown model 4084/25 has been developed which overcomes some of the above-noted deficiencies. That detector is a fully encapsulated module using diode-logic circuitry; buffer amplifiers are employed to isolate the capacitor from the driving circuit and the following circuit, and to provide compensation for variable voltage drops across the diode. The Burr-Brown unit is believed to have certain disadvantages, as for example no capability for repair or alteration of operational response, and no digital output; in the Burr-Brown unit the stored analog signal tends to droop as the capacitor slowly discharges from its state of highest charge.
The present invention seeks to provide a peak detector circuit that overcomes some or all of the above-noted disadvantages. The circuit is made up of standard "shelf" items, thus facilitating repair or replacement of malfunctioning items, and minimizing circuit cost and fabrication time. The circuitry design provides flexibility in operational response to different environmental conditions, i.e. a "fast" detector responding to high frequency signals or a "slow" detector responding to low frequency signals, achieved by the use of components of the appropriate high or low performance characteristics. In a preferred arrangement the peak detector is employed with an analog-digital converter which translates the detector analog output into a digital form that is readily usable in present day computers, and which alleviates the problem of signal "droop".